1893.] the Normal State of the Knee Jerk is altered, 443 



became exaggerated. This exaggeration amounted to clonus in about 

 30 seconds later ; but about 1| minutes later, and after the stage of 

 asphyxial convulsions, the knee jerk was abolished, while the blood 

 pressure was still high, though showing signs of commencing to 

 fall. Artificial respiration was commenced about a minute after this 

 (see fig. 2), and \\ minutes afterwards the knee jerks returned, 

 became exaggerated in about 50 seconds, and returned to their normal 

 state about 2tt minutes later. 



The exact times at which the various phenomena occurred varied 

 in different animals of the same class, and more widely in animals of 

 different classes. Fig. 3 shows the approximate times at which they 

 occurred in one of the rabbits used. In this particular instance the 

 knee jerk became exaggerated about 50 seconds after the tracheotomy 

 tube was plugged, and it was abolished about 70 seconds later. The 

 plug was removed from the tracheotomy tube about 10 seconds after 

 this, and in about 10 seconds the knee jerk returned ; in about 

 12 seconds it became exaggerated, and returned to its normal condi- 

 tion after 60 seconds. In fig. 4, besides the blood and respiratory 

 curves, a tracing of the asphyxial convulsions is shown, as obtained 

 from the extensor muscles of the forearm of the dog, in order to show 

 that the knee jerks were still exaggerated for some time after the con- 

 vulsions had ceased. 



It will thus be seen that exaltation of the knee jerk is a pheno- 

 menon of the so-called first and second stages of asphyxia, while its 

 abolition is related to the third stage of that condition. Figs. 5 and 

 6 are intended to show what relationship exists between the altera- 

 tion in excitability of the spinal centres and that of the cortical cells. 

 Although the cortex exhibits some diminution in its excitability 

 before the knee jerk is lost, yet its excitability is not completely 

 annulled until some time after all attempts to elicit a knee jerk have 

 failed. The preliminary exaggeration of the knee jerk commences 

 to show itself before there is any sign of diminution of the cortical 

 excitability. 



2. The 'Effects of Asphyxia on the Lumbar Centres after Total 

 Transverse Section of the Spinal Cord in the Mid-dorsal Region. — By 

 this means any influence of the cerebrum and cerebellum on the 

 phenomena was entirely excluded. It was found that, with the 

 exception of commencing the experiment with a knee jerk more 

 active than when the cord was not previously divided, the phenomena 

 evoked by the asphyxial state were in every way identical to those 

 observed before the cerebrum and cerebellum were excluded from 

 taking any possible part in, or exerting any influence upon, their 

 production. 



2 i 2 



